Abstract

Measuring solar-like oscillations in an ensemble of stars
in a cluster, holds promise for testing stellar structure and
evolution more stringently than just fitting parameters to single
field stars. The most ambitious attempt to pursue these prospects was by
(Gilliland 1993) who targeted 11 turn-off stars in the open cluster M67
(NGC 2682), but the oscillation amplitudes were too small (< 20 µmag)
to obtain unambiguous detections.
Like Gilliland (1993) we also aim at detecting solar-like
oscillations in M67, but we target red giant stars with expected
amplitudes in the range 50-500 µmag and periods of 1 to 8 hours.
We analyse our recently published photometry measurements, obtained during a
six-week multisite campaign using nine telescopes around the world.
The observations are compared with simulations and with
estimated properties of the stellar oscillations.
Noise levels in the Fourier spectra as low as 27 µmag are obtained
for single sites, while the combined data reach 19micromag, making
this the best photometric time series of an ensemble of red giant
stars. These data enable us to make the first test of the scaling
relations (used to estimate frequency and amplitude) with an homogeneous
ensemble of stars.
The detected excess power is consistent with the expected signal from
stellar oscillations, both in terms of its frequency range and
amplitude. However, our results are limited by apparent high levels of
non-white noise, which cannot be clearly separated from the stellar
signal.